Conventionally, some attempts to add a salt of polyphosphoric acid or a salt of metaphosphoric acid to an oral composition such as dentifrice have been made in order to remove stain or plaque adhered to the surface of teeth. For example, there have been reported an oral composition in which a salt of polyphosphoric acid or a salt of metaphosphoric acid is used together with menthol or anethole (refer to Patent Document 1), an oral composition in which a water-soluble salt of pyrophosphoric acid is used together with a salt of polyphosphoric acid (refer to Patent Document 2), and a tooth cleaning material in which a salt of polyphosphoric acid is used together with a natural scrubbing agent (refer to Patent Document 3).
However, these oral compositions and tooth cleaning materials have some disadvantages such that stain and plaque adhered to the surface of teeth cannot be completely removed from the teeth with a toothbrush or the like, and stain or plaque builds up in spite of daily brushing of the teeth. Such oral compositions and tooth cleaning materials also have another disadvantage such that there can be hardly removed from teeth stain and plaque adhered to the teeth where a toothbrush is difficulty reached.
Accordingly, there has been desired to develop a stain remover which can effectively remove stain and plaque from teeth without the need of brushing the surface of teeth with a toothbrush or the like and also prevents stain and the like from being deposited on the surface of teeth from which once stain and plaque have been removed.
Meanwhile, ultraphosphoric acid has been known to have antibacterial properties, and conventionally has been used as a food preservative (refer to Patent Documents 4 and 5). It has also been reported that the ultraphosphoric acid exhibits an effect of inhibiting change in color of a composition containing tannin (refer to Patent Document 6). However, it has not yet been reported that the ultraphosphoric acid shows a function for removing stain.
Patent Document 1: Japanese Unexamined Patent Publication No. Sho 63-30408
Patent Document 2: Japanese Unexamined Patent Publication No. Hei 8-175966
Patent Document 3: Japanese Unexamined Patent Publication No. Hei 10-182386
Patent Document 4: Japanese Unexamined Patent Publication No. Sho 58-121204
Patent Document 5: Japanese Unexamined Patent Publication No. 2005-80617
Patent Document 6: Japanese Unexamined Patent Publication No. 2002-306126